The general areas of pulmonary host defense and nosocomial infection are being investigated, using Pseudomonas aeruginosa infection as the prototype because of its frequent occurrence in immunosuppressed patients. Specific (immune) and non-specific pulmonary host defenses are being investigated, including: 1) the development of cell-mediated immunity against Pseudomonas antigens, 2) activation of alveolar macrophages by cell-mediated immune mechanisms and non-specific (adjuvant) mechanisms, and 3) recruitment of granulocytes into the lung by bacterial products and alveolar macrophage derived chemotactic factor. Noscomial infection is being studied concurrently in immunosuppressed animals with emphasis on protection against death by passively transferred antibody against a "cross-protective" core antigen, OEP. The efficacy of this vaccine is being investigated in the hope of future clinical use in human subjects.